Al Gore has warned that there is now clear proof that climate change is directly responsible for the extreme and devastating floods, storms and droughts that displaced millions of people this year.

Speaking to an audience of business leaders, political leaders including Scotland's first minister Alex Salmond and green energy entrepreneurs in Edinburgh, Gore said the world was at a "fork in the road".

The former US vice-president and climate campaigner also argued that America has suffered a "breakdown in democratic governance", because members of Congress are obsessed with appeasing special interests in return for campaign funding, rather than confronting climate change.

The former vice president and climate campaigner said that US democracy had been undermined. "In the language of computer culture, our democracy has been hacked," he said.

In a near hour-long speech to the Scottish low-carbon investment conference, Gore said the evidence from the floods in Pakistan, China, South Korea and Columbia was so compelling that the case for urgent action by world leaders to combat carbon emissions was now overwhelming.

"Observations in the real world make it clear that it's happening now, it's real, it's with us," he said. Failing to take action meant the world would face a catastrophe.

He added that nearly every climate scientist actively publishing on the subject now agreed there was a causal link between carbon emissions and the sharp increase in intense and extreme weather events seen across the globe.

"Every single national academy of science of every major country on earth agrees with the consensus and the one's that don't agree with it do not exist. This is what they say to governments: 'The need for urgent action is now indisputable'.

"The scientists have made a subtle but profound change in the way that they speak about the connection between the climate crisis and the extreme weather events. They used to say you can't connect any extreme weather event to climate because there are multiple factors. Now they've changed.

"The environment in which all storms are formed has changed. It's influence is now present according to the leading scientists in all storms, and they speak of relative causation."

Gore said there was now evidence that the globe's hydrological cycles were changing: as the atmosphere and oceans warmed, more water was evaporating and getting stored in the atmosphere. The amount of water vapour over the oceans had increased by 4% in 30 years, particularly around the tropics and sub-tropics.

In turn this fed even heavier and more violent storms and flooding incidents, which in Pakistan displaced 20 million people earlier this year, and which forced out 8.5 million from 13 provinces in China.

This destabilisation of global weather patterns then fed into a complex cycle of more intense and prolonged droughts in drought-prone regions, which in turn caused more frequent and more vicious wildfires, increased desertification of agricultural land, and was now affecting river levels in the Amazon.

There were 387 million people affected by droughts in the first six months of this year. China, Iraq and Iran also recorded their highest ever temperatures during this period. The city of Mohenjo-Daro in Pakistan recorded a temperature of 53.5C, while in the United States, 200 cities broke their highest temperature records this summer. In Texas, 252 out of the state's 254 counties had experienced major wildfires during 2011.

He continued: "They used to say we're changing the odds, we're loading the dice that make it more likely that we'll get extreme weather events. Now the change is we're not only loading the dice, we're painting more dots on the dice. We're not only rolling more 12s, we're rolling 13s and 14s and soon 15s and 16s."

Arguing that the younger generation would demand world leaders showed the "moral courage" to take action, he heaped praise on Salmond, applauding his "vision and leadership" for championing wave, tidal and offshore wind power in Scotland. He said the rapid growth in new renewable technologies gave hope that a successful shift from fossil fuels was possible.

Outside the conference venue, two women employed by the Kreate promotions agency in London handed out anonymously produced leaflets to delegates reproducing media reports of a high court judgment that heavily criticised the accuracy of Gore's 2007 climate documentary An Inconvenient Truth.

Barry Duncan, the manager of Kreate, said their staff had been hired by a client who wanted to remain anonymous, on behalf of another anonymous client, to hand out "leaflets on renewable energy". Duncan said: "This is a bit strange, I totally agree."